1. Field of the Invention
The present invention relates to a fuel cell including an electrolyte electrode assembly and a pair of separators sandwiching the electrolyte electrode assembly. The electrolyte electrode assembly includes an anode, a cathode, and an electrolyte interposed between the anode and the cathode. Further, the present invention relates to a fuel cell stack formed by staking a plurality of fuel cells.
2. Description of the Related Art
Typically, a solid oxide fuel cell (SOFC) employs an electrolyte of ion-conductive solid oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly (unit cell). The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, a predetermined numbers of the unit cells and the separators are stacked together to form a fuel cell stack.
In the fuel cell, an oxygen-containing gas or air is supplied to the cathode. The oxygen in the oxygen-containing gas is ionized at the interface between the cathode and the electrolyte, and the oxygen ions (O2−) move toward the anode through the electrolyte. A fuel gas such as a hydrogen-containing gas or CO is supplied to the anode. Oxygen ions react with the hydrogen in the hydrogen-containing gas to produce water or react with CO to produce CO2. Electrons released in the reaction flow through an external circuit to the cathode, creating a DC electric energy.
In this type of the fuel cell, when a large number of unit cells and separators are stacked vertically, since the weight of the separators and the unit cells is applied to the unit cells at lower positions, the unit cells at the lower positions may be damaged undesirably. In view of the problem, it is desirable to uniformly apply a load to each of the unit cells of the fuel cell. In this regard, for example, the structure disclosed in Japanese Laid-Open Patent Publication No. 2002-280052 is known.
As shown in FIG. 17, according to the disclosure of Japanese Laid-Open Patent Publication No. 2002-280052, a fuel cell 1 is formed by stacking power generation cells 2 and separators 3 alternately in a vertical direction. Each of the power generation cells 2 includes a fuel electrode layer 2b, an oxidant electrode layer 2c, and a solid electrolyte layer 2a interposed between the fuel electrode layer 2b and the oxidant layer 2c. Connection members 4 extend through the outer region of the separators 3 in the stacking direction. The connection members 4 are insulated from the separators 3. The separators 3 are connected to the connection members 4 by fixing members 5. Each of the fixing members 5 is used for fixing one separator 3 or a plurality of separators 3 to the connection members 4.
However, according to the disclosure of Japanese Laid-Open Patent Publication No. 2002-280052, in order to a apply a load to each of the power generation cells 2 uniformly, the connection members 4 and the fixing members 5 are required in addition to the power generation cells 2. Therefore, the horizontal size of the fuel cell 1 is large, and the power generation amount per unit volume of the fuel cell 1 is low. Further, many processes are required for producing the fuel cell 1 including the stack of the power generation cells 2, and the cost of producing the fuel cell 1 is high.